1. Field of the Invention
The invention relates to a control device and control method for a variable valve actuation mechanism that is able to change at least one of the valve operating angle and valve lift of an engine valve.
2. Description of the Related Art
A variable valve actuation mechanism that is able to change the valve characteristics of an engine valve (intake or exhaust valve) is practically used as a mechanism equipped for, for example, a vehicle-mounted internal combustion engine. A variable valve timing mechanism that is able to change the valve timing of an engine valve, a variable valve lift/valve operating angle mechanism that is able to change the valve operating angle or valve lift of an engine valve, or the like, is known as such a variable valve actuation mechanism.
In an internal combustion engine that includes the variable valve lift/valve operating angle mechanism, when the valve operating angle or the valve lift is excessive, the engine valve may interfere with a piston, that is, so-called valve stamp may occur. Then, in such an internal combustion engine, the control range of the valve operating angle or valve lift is limited to a lower limit or below of an interference region in which valve stamp may possibly occur to thereby avoid valve stamp.
On the other hand, in an internal combustion engine that includes both variable valve actuation mechanisms, that is, the variable valve lift/valve operating angle mechanism and the variable valve timing mechanism, a lower limit of the interference region varies in accordance with the set valve timing. Specifically, as the valve timing is changed so that the valve lift center approaches a piston top dead center, the lower limit of the interference region, that is, the upper limit of the valve operating angle/valve lift, by which valve stamp may be avoided, reduces. Then, in such an internal combustion engine, the upper limit of the control range of the valve operating angle or valve lift is changed on the basis of a current valve timing (actual valve timing) to thereby variably control the valve operating angle or the valve lift while avoiding valve stamp.
Incidentally, depending on circumstances, there is a possibility that an actual valve operating angle or an actual valve lift overshoots a target value. In such a case, even when the target valve operating angle or the target valve lift is set to fall outside the interference region, the valve operating angle or the valve lift may fall within the interference region to cause valve stamp.
For example, in a control device for a variable valve actuation mechanism, described in Japanese Patent Application Publication No. 2002-332876 (JP-A-2002-332876), when an actual valve operating angle or an actual valve lift is larger by a predetermined value or above than the target value, a target valve timing is corrected so that the valve lift center is distanced from the piston top dead center to thereby increase the lower limit of the interference region.
With the above control device for a variable valve actuation mechanism, valve stamp due to an overshoot of the valve operating angle or valve lift as described above may be avoided certainly. However, because the target valve timing is corrected each time an actual valve operating angle or an actual valve lift increases by a predetermined value or above than a target value, there is a problem that it is difficult to set an appropriate valve timing in accordance with an engine operating condition.